Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/02—Details
  • A61N1/04—Electrodes
  • A61N1/05—Electrodes for implantation or insertion into the body, e.g. heart electrode
  • A61N1/0526—Head electrodes
  • A61N1/0541—Cochlear electrodes

Definitions

• the present invention relates to the structure, method of use and method of manufacture of an implanted hearing prosthesis.
• the cochlea is a long narrow duct wound spirally about its axis for approximately two and a half turns.
• the fluid filled cochlea transmit waves in response to received sounds and in cooperation with the cochlear duct, function as a transducer to generate electric impulses which are transmitted to the cochlear nerves and thence to the brain.
• an auditory prosthesis for the deaf therefore requires a suitable stimulation electrode capable of stimulating the auditory nerves.
• a design of an implantable hearing prosthesis that is currently available for use in patients includes a transmitter, a receiver and an external battery such that the receiver interacts with electrodes placed surgically in the cochlea (Hochmair et al., U.S. Patents 4,284,856 and 4,357.497) so as to selectively stimulate the wall of the cochlea in accordance with the frequency response thereof.
• the electrodes are typically contained in an electrode carrier that is circular in cross-section and made of a flexible material but is of sufficient stiffness to be guided into the cochlea in the desired coiled shape (Hochmair-Desoyer et al., Annals of the New York Academy of Sciences 405: 173-182 ( 19??)).
• a flexible eight channel scala typani electrode carrier was developed which was circular in cross section and tapered slightly to the tip, having a diameter at each contact site along its length that was slightly smaller then the smallest diameter observed at the corresponding length in human scala tympanies.
• the electrode carrier contained 16 Teflon-insulated 90% Pt-10% Ir wires with a diameter of 1 mil embedded in a silastic body.
• the contact members were arranged in two rows on opposite sides of the electrode carrier.
• each wire terminated in a ball having a diameter of 0.35 mm which protruded just slightly from the electrode carrier so as to form the contact member.
• This protruded form of the contact member was later described by Loeb et al. (1983), Med. and Biol. Eng. and Computing 21 :241.
• This design of electrode carrier was capable of being placed up to 22 mm into the cochlea.
• Clarke in the J. Laryngology and Otology 93: 107-109 ( 1979), where contact members were formed from 0.3 mm wide rings of platinum encircling the electrode carrier.
• the prosthesis described by Clarke was inserted up to 20 mm into the cochlea but insertion was restricted by the rigidity of the device that resulted from the spaced platinum collars along the length of the electrode carrier.
• only a minor portion of the electrical current released at the contact ite could reach an auditory nerve because the current would be released over an arc of 360° to achieve contact with a neuron positioned at one site only in the arc. Consequently, the device of Clark was relatively energy inefficient.
• a hearing prosthesis for implantation into a subject includes a flexible electrode carrier adapted for insertion into the cochlea of the ear
• the electrode carrier has an oval cross-section, the cross section having a long axis
• the carrier also has a plurality of discrete shaped contact member pairs arranged at a predetermined spacing along a fraction of the length of the electrode carrier Each contact member pair is superficially placed on the carrier and comprises a first contact member diametrically opposed to a second contact member on the long axis of the cross-section
• each contact member has a base portion and an extended portion, wherein the base portion is embedded within the electrode carrier, the extended portion having a top that is substantially continuous with the exterior surface of the electrode carrier
• the contact member may be placed within wells located diametrically opposite on the long axis of the cross section and the contact member in such well may further contain an expandable extension component that may be caused to expand within the cochlea, thereby causing the contact member to be approximately placed in close contact with an auditory nerve
• a further embodiment of the invention is a method for producing a prosthesis, that includes forming a flexible electrode carrier adapted for insertion into the cochlea of the 5 ear, the electrode carrier having an oval cross-section, the cross-section having a long axis; and placing a plurality of discrete shaped contact member pairs at a predetermined spacing along a fraction of the length of the electrode carrier, causing each contact member pair to be superficially placed on the carrier and comprising a first contact member diametrically opposed to a second contact member on the long axis of the cross- section.
• a further embodiment of the invention is a method for implanting a hearing prosthesis in a subject that includes selecting a flexible electrode carrier adapted for insertion into a cochlea, the electrode carrier being oval in cross section; and having a plurality of discrete shaped contact member pairs along the surface of the electrode carrier, each contact member pair having a first and a second contact member such that the first contact member is diametrically opposed to the second contact member on the cross-sectional long axis, and inserting the flexible electrode carrier into the cochlea so that one contact member in each pair is adjacent to at least one auditory nerve.
• a further embodiment of the invention is a method for manufacturing an individually customized implantable hearing device for a subject that includes measuring the evoked auditory nerve potential of the cochlea; determining the location and density of responsive neurons; and preparing an electrode carrier as described above, having suitably placed contact members.
• Figure la is a top view of a metal foil that has been pressed out of a larger sheet in a semi-oval shape.
• Figure lb shows a cross section through the metal foil.
• Figure 2a is a top view of the metal foil after molding into a hat shape while 2b shows a cross section through the contact member.
• Figure 3 is a cross-section through the electrode carrier showing the placement of two opposing contacts on the long axis.
• Figure 4 (a)-(c) show three separate cross sectional views of the electrode carrier during manufacture where the electrode carrier is placed in a mold having 8 pairs of vacuum holes spaced regularly over different lengths along the electrode channel for placing the contact members.
• Figure 5 shows an outline of the oval cross section of an electrode carrier with the marked location of contact members.
• An electrode carrier is defined here and in the claims as the body of the implantable device.
• a contact member is defined here and in the claims as the terminal component of the electrode.
• An electrode carrier has been designed as shown in Figures 4 (a)-(c).
• the electrode bears a marker (9) at a predetermined distance from the tip of the electrode carrier to delimit the region of the carrier that should not be contacted by the surgeon during placement of the prosthesis. From the marker, toward the tip of the electrode carrier, the diameter of the electrode carrier tapers to about 1.5 mm at ( 10).
• the distance between ( 10) and (9) and the relative increase in diameter as well as precise location of the marker directly impact the formation of kinks in the electrode during implantation. It is desirable to limit the occurrence of such kinks.
• the marker is located at a distance of about 10 mm from the closest contact member and has a diameter of approximately 3-4 mm.
• the minimum diameter of the electrode carrier is 1-2 mm or more particularly 1.5 mm in this embodiment, increasing in diameter to about 3-4 mm (more particularly 3 mm)over a distance of about 3-5 mm (more particularly 3.5 mm).
• equivalent minimum values for the diameter along the short axis (12) and the long axis (1 1) may be selected to maximise the depth of insertion.
• Contained within the electrode carrier is a series of wires that terminate, at selected sites on the surface of the carrier, to form contact members.
• the wire (Pt-Ir(25%)) has a 25 ⁇ m diameter with a 5 ⁇ m Teflon insulation layer.
• the thickness of the wire is approximately inversely related to the flexibility of the electrode carrier so that a thick wire causes the electrode carrier to be less flexible then it would be otherwise.
• the electrode carrier is formed from a polymer having a flexibility profile that is sufficient to permit the placement of the carrier at a distance greater than 24 mm into the cochlea.
• a silicon elastomer is used that is supplied by Applied Silicon in California and is called Silastic LSR40 having a ratio of buffer A and B of 10: 1.
• the wires within the electrode carrier are attached to contact members that are placed at selected locations along the electrode carrier as shown in Figure 4.
• the contact members are orientated on the surface of the electrode carrier so as to maximize the proximity of each contact member with neurons. This is further accomplished by any or all of the considerations itemized below: maximizing the penetration length of the electrode carrier within the cochlea of individual patients, the maximum length being 34 mm, the entire length of the cochlea itself. The optimum maximum length may vary according to the differing amounts of ossification of the cochlea as well as the location of the functioning neurons; introducing flexibility in the design of the electrode carrier to accommodate inter- patient variability in the extent of functioning neurons in the cochlea; and selecting a cross sectional shape of the electrode carrier such that at least one contact member in each pair is located adjacent to the functioning neurons.
• an advantage of utilizing the maximum length of the cochlea includes access to locations where the induced pitch precept corresponds to the pitch precept naturally elicited in the normal hearing person by an incoming sound of the frequency which is the "best" frequency.
• the "best" frequency is here defined as the frequency for which the turning curve of single auditory nerve fibers, the threshold of hearing for an acoustic signal, is lowest. In this manner, naturally sounding hearing sensations can be obtained and the length of period of increasing speech perception until saturation is reached will be shorter.
• the electrode carrier is oval in cross-section thereby having a long axis on which contact member pairs placed in a diametrically opposed position
• the oval cross-section of the electrode carrier provides a means for introducing the prosthetic device in a single orientation such that the contact members are always located in a north and south position on the oval perimeter
• the electrode carrier having this shape may not twist during insertion in contrast to the circular designed electrode carriers of the p ⁇ or art
• the contact members may be located as desc ⁇ bed above in a north and south orientation on the long axis of the oval electrode carrier within wells, the wells optionally containing an expandable extension of the contact member
• the expandable extension may be positioned in a well such that when the electrode carrier is placed in the cochlea, the contact member becomes raised so as to be approximately touching the auditory nerves
• the raising of the contact members in an expandable extension may be accomplished for example, by osmosis or by the hydration of a polymer
• the expanded component may be finger-like in
• Figures 1-3 describe embodiments of the manufacture and placement of contact members in the electrode earner
• an oval piece (1) is punched out of a sheet of foil
• This punched out form has a thickness of 0 5 mm and a radius of curvature of 0 3 mm ( Figure lb).
• Figure 2a shows the oval piece of metal foil after it has been pressed over a mold, where the mold imposes a shape on the foil which includes a base portion (2) and an extended portion (3) such as exemplified by a hat-shape, where the base portion has a larger perimeter then the extended portion.
• the extended portion may be symmetrically disposed above the base portion as shown in Figure 2(a) although the extended portion may alternatively be asymmetrically placed on the base portion in certain embodiments.
• the base portion may have a similar or equal radius of curvature to the extended portion and may also have a similar or equal thickness to the extended portion.
• Figure 3 shows the orientation of the contact member in the electrode carrier.
• the base portion (2) is embodied within the polymer of the electrode carrier and the surface of the extended portion (5) is substantially continuous with the surface of the electrode carrier (6).
• the extended portion is hollow where the cavity (4) extends through the base portion.
• Figures 4(a)- (c) show the alignment of eight contact members pairs along the length of the electrode carrier (7) [(A), (B) and (C)] such that the distance between each contact is varied according to the overall length of the electrode carrier.
• each contact surface (5) is placed at a distance of 1.6 mm from the adjacent contact member, where the electrode carrier is 22.2 mm in length.
• each contact member surface is placed at a distance of 2.8 mm from the adjacent contact, where the electrode carrier is 30.8 mm in length.
• each contact surface is placed at a distance of 3.80 mm from the adjacent contact member, where the electrode carrier is 30.76 mm in length.
• the number of pairs of contact members may vary according to the condition of the cochlea.
• electrode carriers may have 4, 5, 6, 7, 9, 10, 11, 12, or more pairs of contact members, for example in a range of 4-16 pairs of contact members.
• the distance between adjacent pairs of contact members may vary according to the number of pairs of contact members located on the electrode carrier and the condition of the cochlea in the subject.
• the cross section of the electrode carrier as shown in Figure 4 may be elliptical or oval in shape (Figure 5).
• This cross sectional shape has a characteristic long axis ( 1 1) and a short axis (12).
• the oval shaped cross-section of the carrier facilitates the insertion of the electrode carrier into the cochleal canal by permitting increased bending of the electrode carrier along the short axis of the cross section.
• the consistent orientation of the oval electrode carrier is not possible with the cylindrical electrodes of the prior art.
• the contact members are placed in pairs along the electrode carrier such that one contact member in the pair is placed at a location on the surface of the carrier that is opposite to the surface location of the second contact member in the pair on the long axis.
• This arrangement permits at least one contact member to be adjacent to the nerves to be stimulated. This improved localization of the contact with regard to the auditory nerves makes possible the focussed delivery of current through a relatively small arc and thereby requires a reduced threshold of current required to stimulate the nerves. The advantages of reduced stimulatory current requirements is apparent in the reduced size and increased longevity of the battery that accompanies the prosthesis.
• a mold (8) is used as shown in Figure 5, which is formed of two halves that are mirror images of each other.
• the mold has fenestra along its' length to which vacuum lines are connected (9).
• the metal foil contact as shown in Figure 2 a and b are placed into the fenestra in each mold half under vacuum.
• the electrodes to be connected to the contact members are placed within a longitudinal hollow cavity in the mold and a single electrode wire is positioned over each fenestra and joined to the metal foil contact.
• the two mold halves are then put together and injected with a polymer (preferably a silicon elastomer containing 10 g of A and 1 g of B solution) [Silastic LSR 40 Applied Silicon, California].
• the proper proportion of A and B are selected to provide sufficient flexibility necessary for insertion of the electrode carrier into the cochleal canal at a depth in the range of up to 32 mm. All of the above cited references and publications are hereby inco ⁇ orated by reference.

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• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Cardiology (AREA)
• Heart & Thoracic Surgery (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Radiology & Medical Imaging (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Prostheses (AREA)
• Electrotherapy Devices (AREA)

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• 1997
  • 1997-02-26 AT AT97915636T patent/ATE300265T1/de not_active IP Right Cessation
  • 1997-02-26 JP JP52994697A patent/JP4043049B2/ja not_active Expired - Lifetime
  • 1997-02-26 AU AU23043/97A patent/AU722787B2/en not_active Expired
  • 1997-02-26 EP EP97915636A patent/EP0884991B1/de not_active Expired - Lifetime
  • 1997-02-26 DE DE69733813T patent/DE69733813T2/de not_active Expired - Lifetime
  • 1997-02-26 ES ES97915636T patent/ES2247624T3/es not_active Expired - Lifetime
  • 1997-02-26 US US08/807,038 patent/US5876443A/en not_active Expired - Lifetime
  • 1997-02-26 WO PCT/IB1997/000415 patent/WO1997030670A1/en active IP Right Grant
  • 1997-05-01 TW TW086105770A patent/TW337486B/zh not_active IP Right Cessation

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